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One Day One Command
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, >>, | —  Redirection Operators.

Summary:

By using some special notation, we can redirect the output of many
commands to files, devices, even to the input of other commands and
pass the output of one command as input to another command. There are
3 Type redirections are available in shell:

1) Standard Output, 2) Standard Input and 3) Pipe

Examples:

$ ls > MyFile — Redirecting the std output of ‘ls’ to a file.

$ ls >> MyFile — Append the redirected ‘ls’ output to a file.

$ ls NoDir 2> MyFile — Redirect the std errors to a file. (TRY: Just

                       remove the 2 and check the output).

$ touch a b — Create 2 dummy file for testing.

$ ls a b c d > MyFile 2>&1 — Redirect both std output and std error

                             to a file.

$ sort < NameList -- Redirect the file 'NameList' as the input to the

                    sort command.

$ sort file — Same as above. But here output is also

                           redirected to file.

$ ls -1 | sort | less — Output of ‘ls’ is piped to ‘sort’ as an input

                   & output of ‘sort’ is piped to ‘less’ as an input.

Filter Programs performs operations on input and writes the result to

the standard output. Filters are very useful in redirection. Examples:

sort, tee, grep, less, head.

Read: info bash